We have established that microangiography is a highly suitable method to obtain a complete picture of the blood microcirculation of the lymph node. We have described a definite and recurring pattern of the blood microvasculature within the undifferentiated lymphoid tissue, the primary and secondary nodules, the pseudonodules, and the medullary cord. In our experiments in rabbits, we found significant changes in the blood supply within the lymphoid tissues and nodules during the primary immune response. In preliminary experiments, we are studying the changes in the blood microcirculation in the lymph node in experimental xanthomatosis. Other preliminary experiments on rat lymph nodes, concerning the effects of local irradiation on the blood microcirculation, are currently being evaluated.